We used cultures of sympathetic neurons from chicken embryo ganglia as an assay for neurotrophic activity. Introduction of radioactive tracers has been developed to facilitate quantification of neurotrophic activity. We looked for neurotrophic activity in CSF of normal volunteers, neurologic and psychiatric patients. There was no evidence of neurotrophic activity in most of the CSF tested. However, CSFs of some schizophrenics were found able to support neuronal survival in culture. This activity was independent of neuroleptic treatment but was positively correlated with ventricular enlargement of the brain.